Composition, structure and tectonic setting of the Southern Kangurtag accretionary complex in Eastern Tianshan, NW China: Implication for accretionary process of Central Asian Orogenic Belt

The Kangurtag belt in the Eastern Tianshan, connecting the Dananhu Arc with the Central Tianshan Arc, contains diagnostic rocks of accretionary origin, and thus it is a key to the evolution of the North Tianshan Ocean (NTO), which is the southern branch of Paleo-Asian Ocean. The Southern Kangurtag belt is composed of Ocean Plate Stratigraphy and two types of mélange. Type I mélange consists of fossiliferous limestones on top of E-MORB-type pillow basalts, flanked by olistostromes, turbiditic sandstones, pelagic cherts and mudstones. This rock association resembles that of the Ocean Plate Stratigraphy on a seamount. In Type II mélange, N-MORB and ribbon cherts were dismembered and embedded in clastic matrix, showing a "block-in-matrix" structure. The lithologies and structures of the Southern Kangurtag belt suggest an accretionary origin with a top-to-the-north tectonic vergence. Detrital zircons of 4 sandstones from Devonian and Carboniferous strata within the mélanges have predominant age populations of 410-430 Ma, and some Precambrian clusters around 0.8-1.2 Ga, 1.5-1.6 Ga, 1.8-2.0 Ga, and 2.5 Ga. The ɛHf(t) values of Phanerozoic zircons range from -25.1 to +8.6. Since the provenance of detrital zircons from the Northern and Southern Kangurtag belt show discrepant population patterns and Hf isotopic compositions. Thus, such age patterns and Hf isotopic data indicate these sedimentary successions deposited on fore-arc of the northern margin of the Central Tianshan Arc. The youngest detrital zircon age of 316.6 Ma provides an upper limit for the Southern Kangurtag accretionary complex. Therefore, we suggest that the Southern Kangurtag belt comprises a accretionary complex developed during southward subduction of the NTO beneath the Central Tianshan Arc. The subduction of the NTO may have lasted to the late Carboniferous-late Permian.